The invention relates to a process for producing cathodes with integrated grids.
The use of cathodes of this type has been made necessary by the continual increase in the power level of electron tubes, particularly for ultra-high frequencies, in which the power of the electron beam has become such that the fraction of the latter intercepted by the grids placed on its path can be sufficient to considerably deteriorate their characteristics (dimensions, alignment, mechanical behaviour) and even prejudice their service life.
One of the main problems which occur in this connection is that of the first two grids, generally called G.sub.1 and G.sub.2. These grids, which respectively ensure the control and acceleration of the electron beam emitted by the cathode, must have aligned bars, the first casting a shadow on the second, thereby preventing an excessive interception of the beam by the latter. When the first of these grids G.sub.1 is incorporated into the cathode, this condition is more easily fulfilled. Due to its integration, grid G.sub.1 is protected from such an interception.
According to this procedure, grid G.sub.1 is etched on the emissive face of the cathode on which solid portions constitute areas which are protected from the emission surrounding the emissive areas in accordance, for example, with a system of meshes arranged in rectangular columns and lines. The alignment of the second grid G.sub.2 with the first is then made much easier.
The problems include that of the non-emissivity of the incorporated or integrated grid, despite its proximity to areas which are rich in emissive material and in particular the problem of the choice of its constituent material for this purpose.
In the prior art this problem has been solved in various ways. Various process have also been proposed for producing cathode with integrated grids.